USB recognizes three different power states: power-on, suspended, and power-off. The question is: Should it be possible to use the power-off state as a surrogate for an extremely low-power suspend state (like suspend-to-disk)? Unfortunately the current API doesn't allow for such
Erm, "suspend-to-disk" isn't really a suspend state, and it can only fake things out so far ... in particular, not to the extent of making arbitrary devices act as if they've retained power (and associated state).
distinctions; the suspend() method in usb_driver doesn't include an
argument to indicate which sort of suspend is about to occur.
Probably an error. I see no good reason to drop the argument during the call chain.
Although I'm not aware of the original design decisions, I imagine the API was intended to follow the USB specification, which has only one suspended state.
Not an error; it's as Alan said. If we stick to "USB suspend" as the only suspend state, we don't have to re-architect anything and try "improve on" (== diverge from) this industry standard spec.
The only reason to have such an argument in USB is sort of a botch in the Linux PM APIs ... it assumes that there are multiple levels of suspend. That's nonsense in this case, and many other non-ACPI cases. So a number has to be stored, which doesn't cause too much trouble when something starts reasoning as if all the world is ACPI. The number is accordingly "3", the deepest "suspend" in ACPI.
- Dave
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